A currently widely used antenna of a mobile communication base station generally has a structure in which a plurality of radiating elements is vertically arranged which can transmit or receive an electric wave using two polarized waves (generally, X-shaped polarized waves) perpendicular to each other. A plane of polarization of the X-shaped polarized waves is basically arranged to be inclined at an angle of +45 degrees or −45 degrees with respect to a horizontal or vertical plane.
In this case, the antenna commonly includes a Remote Azimuth Steering (RAS) device for remotely controlling azimuth steering and a Remote Azimuth Beam-width (RAB) device for remotely controlling an azimuth beam-width as well as a Remote Electrical Tilt (RET) device that is remotely controllable and electronically controls a down tilt angle. An example of an antenna including the devices is disclosed in Korean Patent Publication No. 10-2010-0122092 first filed by Amphenol Corporation (published on Nov. 19, 2010 and entitled “Multi-beam Antenna with Multi-device Control Unit”; inventors Gregory Girard and Frank Soulie).
For control of the RET device, the RAS device, and the RAB device, Antenna Interface Standards Group (AISG) v2.1.0 was recently devised, and a communication scheme through 3rd Generation Partnership Project (3GPP) protocol was also developed.
Referring to FIG. 1, according to the AISG standards, the RET control is mainly divided into a control by a primary station and a control by a secondary station. As a master part, the primary station refers to a part, such as a Master Control Unit (MCU) 22, which may be provided in a main system of a base station to transmit a control signal, and as a slave part, the secondary station refers to a part, such as an RET 14 and an ALD modem 13, which may receive the control signal to perform an operation according to the corresponding control signal. A mobile communication base station may generally include an antenna system installed at a higher place such as a building or pillar, a main system of the base station installed on the ground, and a feeder cable for connecting the antenna system and the main system, in which the primary station may correspond to the main system of the base station, and the secondary station may correspond to the antenna system.
Referring to FIG. 1, a base station main unit 21 transmits an RF signal through a feeder cable, and the MCU 22 transmits a DC signal and an RS485 communication signal to drive the RET device 14. The signals transmitted from the base station main unit 21 and the MCU 22 are converted and synthesized into DC signal+RF signal+OOK signal through a Bottom ALD modem 23. The synthesized signal is transmitted to the lower end of the antenna through the feeder cable again. A Top ALD modem 13 of the antenna system filters out DC signal+OOK signal and provides the filtered signal to the RET device 14 to help the RET device 14 receive a command. In addition, the modem 13 provides an RF signal to transmission/reception antennas 11 and 12 of the antenna 10. The signals received by the transmission/reception antennas 11 and 12 of the antenna 10 are provided to the base station main unit 21 through the feeder cable.
FIGS. 2 and 3 illustrate structures in which an RET device, an RAS device, and an RAB device are installed in an antenna according to the AISG rules. In FIG. 2, an RET device 14, an RAS device 15, and an RAB device 16 are connected to the outside through a plurality of AISG connectors installed on a lower cap of an antenna 10 and are connected to one another by the daisy chain method using AISG cables through the AISG connectors. In this case, the connection may be made to primarily provide an external DC+RS485 signal to the RET device 14.
In FIG. 3, an RET device 14 is connected to the outside through an AISG connector installed on a lower cap of an antenna 10, and the RET device 14, an RAS device 15, and an RAB device 16 are connected to one another in an enclosure of the antenna 10 by the daisy chain method using AISG cables.
However, according to the current AISG rules, for RET, RAS, and RAB control, the RET device 14, the RAS device 15, and the RAB device 16 have to be provided in the antenna 10 and connected to one another using the AISG cables as described above, thereby causing a cost increase due to device installation and problems involving installation space and weight. In addition, the main system of the base station has to perform control signal transmission/reception procedures for the RET device 14, the RAS device 15, and the RAB device 16, respectively, thereby resulting in complex communication procedures. The problems are more serious for the dual, triple, and quad-band antennas.